With controversy over iron mining in northern Wisconsin subsiding in recent months, a Canada-based company has resurrected plans to develop an open-pit mine in Michigan's Upper Peninsula, a few hundred feet from the state border.

Aquila Resources Inc. says it will invest more than $300 million to extract gold, zinc, copper and silver along the Menominee River, which divides northeastern Wisconsin from Michigan and flows into Green Bay.

Michigan regulators, who must review permits for the project, held their first public hearing last week. While authorities in Madison have no regulatory oversight, a mine would have clear implications for Wisconsin and Lake Michigan:

■ Wastewater would be treated and discharged to the Menominee, a river over which Wisconsin and Michigan share jurisdiction. Wisconsin Department of Natural Resources officials have conferred with Michigan about water quality standards and the mine's potential to pollute state waters.

■ Wisconsin's Menominee tribe, headquartered in Keshena about 50 miles away, says the river corridor is its original tribal home. Members are worried about environmental problems and the mine's impact on burial grounds and other historic cultural resources.

■ Nearly $8 million — much of it federal dollars — has been invested in fish passage equipment and technology on dams near the mouth of the river. Five dams on the river have prevented sturgeon from migrating upstream from the lake to spawn. The fish passage project is designed to introduce more lake sturgeon to Lake Michigan.

In Wisconsin in February 2015, Gogebic Taconite announced it was shelving plans to construct an iron ore mine in Ashland and Iron counties. The decision ended — for now — debate over potential economic benefits and environmental costs of the project.

Toronto-based Aquila's plans for its Back Forty Project on 580 acres are igniting the same concerns. If approved by regulators later this year, the company said, production could begin in late 2019 or early 2020.

The several hundred people who appeared Tuesday at a public hearing in Stephenson, Mich., appeared to be evenly split with supporters and opponents, according to the EagleHerald in Marinette and Menominee, Mich.

An Aquila-commissioned study by UM-Duluth said the project would generate more than $20 million in new tax revenue for federal, state and local governments annually, and more than $16.5 million in royalties would flow to Michigan's state government over the 16-year life of the mine.

In addition to 1,330 construction jobs, it would generate about 450 new jobs at the mine and surrounding four-county area, including Marinette County in Wisconsin, the study found.

But others are worried about natural resources.

The River Alliance of Wisconsin is raising concerns about the mine's potential to pollute the river and harm efforts to boost the sturgeon population — the state's largest species of fish that can grow to more than 5 feet.

The Madison-based group has played a significant role in the sturgeon-passage project, which has received $6 million from the U.S. Environmental Protection Agency and the National Fish and Wildlife Foundation, and nearly $1.8 million from Eagle Creek Renewable Energy, a dam owner.

At a dam between Marinette and Menominee, the structure has been retrofitted to let sturgeon ride an elevator from the river bottom to a holding area where the fish are inspected, tagged and trucked upstream to spawn.

Biologists believe the Menominee is the largest source of sturgeon for Lake Michigan. By 2020, officials predict improvements in fish passage upstream and downstream could add tens of thousands of sturgeon to the lake.

"If there is a spill at the mine, it could harm the very sturgeon that we are trying to bring back," said Denny Caneff, executive director of the River Alliance. "One stupid mistake could snuff out everything."

Barry Hildred, Aquila's chief executive officer, said the company intends to avoid such mistakes, noting that $70 million has already been spent on planning and scientific reports for the company's mining application.

"It is paramount to us that we operate in a very environmentally friendly and very safe way," Hildred said.

In Wisconsin, the Flambeau mine, a gold and copper mine on the Flambeau River near Ladysmith operated from 1993 to 1997 and, according to the DNR, is the only metallic mine in Wisconsin to be successfully permitted and reclaimed under the state's current metallic mining laws. Some environmentalists have alleged the site remains polluted.

In 2010, Hudbay Mineral Inc. of Toronto, then the leading partner in the Michigan project, said it was putting the mine on hold. However, Aquila's interest in the project never wavered, Hildred said.

Publicly traded Aquila raised nearly $21 million, the company announced on April 1. Hildred said it still must raise $250 million to $300 million to construct the mine. Shares closed Friday slightly under 17 cents per share.

In November, the company submitted an application to Michigan, including information on the geochemistry of waste rock, hydrogeology, groundwater and air quality modeling and reclamation plans. Much of the technical work was performed by Foth Infrastructure & Environment of Green Bay.

The Back Forty's 83-acre pit would lie as close as 150 feet from the banks of the river in the mineral-rich Penokean volcanic belt. Forty percent of the value of the minerals would come from gold deposits, according to company financial documents.

Aquila documents also show that it would remove 532,000 ounces of gold, 721 million pounds of zinc, 74 million pounds of copper, 4.6 million ounces of silver and 21 million pounds of lead.

Gold is currently selling for about $1,100 an ounce.

The minerals are in sulfide rock deposits that produce acidic water when exposed to air and water. Also cyanide, a naturally occurring chemical that is toxic in large doses, is used in a diluted form during processing to separate gold and silver particles from ore.

Water at the mine and adjacent plant would be cleaned in a wastewater treatment plant before it is discharged to the river or can seep into groundwater. Michigan Department of Environmental Quality officials have agreed to impose the stricter of water quality standards between the two states.

Aquila will have to demonstrate to the Michigan's DEQ that it will protect surface water and groundwater from acid mine drainage, cyanide and other pollutants.

Will Aquila be able to do that?

"We aren't sure yet," said Joe Maki, a geologist with the DEQ who said the agency will spend much of 2016 going through thousands of pages of the company's application to answer that question.

Aquila also submitted archaeological data, but a member of Menominee tribe said tribal members were not consulted. Tribal member Guy Reiter said a burial site and prehistoric agricultural fields lie within in the boundary of the project.

"We have lived on that river for 10,000 plus years, and those cultural resources are ours," said Reiter, a mining opponent.

Hildred said his company plans to meet with the tribe soon, and with other groups that have expressed their concerns.

About Lee Bergquist

Lee Bergquist covers environmental issues and is author of "Second Wind: The Rise of the Ageless Athlete."